Refrigerant-containing systems, such as air conditioning, usually contain a desiccant to prevent moisture accumulation in the refrigerant. If moisture accumulation in the refrigerant is not avoided, valve and control member corrosion leads to inevitable systems malfunctions. As a practical matter, no desiccant has infinite capacity, and as a result it is customary for a visual moisture indicator to be included in a refrigerant-containing system. Ordinarily, visual moisture indication is provided by means of a receptacle which cooperates with an instrument that samples refrigerant from the compressor. Such a receptacle contains a chemical compound or composition which undergoes a color change when it is exposed to moisture.
Although a number of chemical compositions change color in the presence of moisture, particularly well suited chemical salts for moisture indication are cobaltous chloride (CoCl.sub.2) and cobaltous bromide (CoBr.sub.2). Cobaltous chloride is relatively inexpensive and yet provides distinct, reversible color change upon hydration to CoCl.sub.2 *6H.sub.2 O. Cobaltous chloride is blue in its dry state, but its color rapidly changes to pink (a good "alarm" hue) in the presence of moisture. When hydrated CoCl.sub.2 is dried, the CoCl.sub.2 turns blue again. CoBr.sub.2 anhydrous is green, but turns (reversibly) yellowish salmon pink in the presence of moisture.
As an economic and practical matter, CoCl.sub.2 or CoBr.sub.2 (or any other color changing moisture indicating composition) is typically adhered to a particulate carrier. The combined cobaltous-salt-coated particulate is then provided, by means of disposable or reusable prepackaged tubes, etc., to the receptacle in the instrument which samples the refrigerant or other moisture sensitive fluid.